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Traceable Scanning Probe Nano-Characterization

Summary

Research and development of rigorously SI traceable nano-characterization instrumentation, measurements, and procedures to enable a fundamental understanding of scanning probe interaction and characterization for nanostructures. A primary goal is to develop traceable reference measurements and artifacts to enable manufacturing of sub 10 nm structures and devices.

    Description

    T-AFM laser path and stage. Motions in three axes are monitored by displacement interferometer.

    Figure 2. T-AFM laser path and stage. Motions in three axes are monitored by displacement interferometer.

    The project provides the metrological underpinnings and reference measurements that support other instruments used in nanoscale metrology for a wide range of applications in optics and photonics, advanced IC characterization, and biotechnology industries among others (internal and external customers). The activities which span from fundamental understanding of tip SPM image formation to instrument development, to standards development, are motivated by the need to provide SI traceable dimensional measurements for nanoscale features, supported by rigorous uncertainty specifications to users. The project currently has the only dimensional metrology AFM at NIST with direct traceability to the SI meter, and is in line with NIST and PML's priorities in disseminating traceable measurements for nanoscale features.

    The best measurement uncertainty for a height sample using the T-AFM is 0.03 nm (K=2). Customers and collaborators who have used the NIST AFM calibration service include Bruker- Nano, NanoDevices, VLSI, Advanced Surface Microscopy, among others. SI traceable measurements for calibration sample vendors help underpin the national measurement system since these values are propagated to thousands of samples a year. These samples are then used on regular basis by the end users for nanoscale characterization and instrument evaluation.

    We participate and contribute to standardization efforts (through ISO and CCL) for scanning probe microscopy. This includes procedures and documentary standards for AFM nanoscale length calibration, and standards aimed at understanding instrument behavior and performance.

    NIST-traceable AFM
    Figure 1. (a) Solid model of the NIST Traceable –Atomic Force Microscope (T-AFM) (b) T-AFM image of sub-nm steps on Si (100) atomically flat surface.

    Major Accomplishments

    2017/2016

    • Bilateral Comparison with PTB on TEM/Si lattice based tip calibrations.  To confirm consistency of the independent TEM/Si lattice based tip calibrations developed at NIST and PTB, we completed a comparison of these calibration standards (the NIST SCCDRM and the PTB IVPS-PTB).  Agreement is within uncertainties and at the 1 nm level.  (As part of the collaboration, a joint NIST/PTB paper was published in Measurement Science and Technology)
    • Development of tip characterizers and methods: Developed a procedure to characterize CD-AFM tips using SiSiO2 superlattices tip characterizers. This is the first time such characterizers have been used for CD-AFM tip. The procedure requires fewer steps than current methods and has uncertainties below 1 nm. This was part of a NIST/AIST collaboration. (Journal paper in Ultramicroscopy)

    • Piloting of inter-laboratory circulation of AFM linewidth samples. We are the pilot laboratory for the BIPM inter-comparison for linewidth NANO6. The comparison is organized through BIPM/CCL/WG-N.  The comparison evaluates the capability of different national measurement institutes to measure linewidth with atomic force microscopes, and the consistency of the results.

    • CD-AFM Contour Measurement: developed a new contour measurement algorithm technique for measurements of arbitrary shaped nanostructures using multiscale information. Contour data allows the use of a comprehensive body of information beyond critical dimensions to make sure that printed IC features represents the intent of the designer. Although data from CD-AFM are three dimensional in structure, the planar two-dimensional data required for contour metrology is not easily extracted from CD-AFM data.  The method we developed allows extraction of CD-AFM data for use as contours. (Journal paper published in JM3)

    • Completed bilateral comparison of photomask linewidth with PTB.  First round results published at SPIE Scanning Microscopies conference in 2015.  Second round results in preparation for JM3.

    • Chair: International Roadmap for Devices and Systems (IRDS Metrology Technical Working Group (Orji). Coordinating the 2017 IRDS Metrology roadmap. This includes helping align metrology roadmap requirements for next generation computing needs with future requirements such as the ones outlined in the National Strategic Computing Initiative (NSCI).    Align with other roadmap organizations on metrology requirements for next generation computing.

    • Co-chair of CCL/WG-N: (Dixson) Currently leading working group on dimensional nanometrology.  The co-chairs (NIST and PTB) of this group will publish a BIPM mise en pratique about the use of AFM and TEM to realize the meter through the silicon lattice constant – based on prior work by both NIST and PTB.

    • Published a journal paper on uncertainty techniques in calibration of CD-AFMs using TEM. The paper outlines techniques for CD-AFM calibration using transmission electron microscopy, measurement, analysis, and uncertainty development.

    2015

    • Validated basic model of CD-AFM lateral tip dither using very large tips (high lateral stiffness) to place lower bound on tip bending. 

    • Completed upgrades of T-AFM mini-environment to current performance of +/- 3 mK - 

    2014

    • Developed a CD-AFM tip characterization technique using SiSiO2 superlattices – Sept 2014
    • Characterized and qualified a next generation Traceable -AFM -Jan 2014
    • Co –wrote new sections and coordinated the roll out of the 2013 edition of the ITRS Metrology chapter. - March 2014

     

    Technical Goals:

    • Develop and deliver measurements, standards, and infrastructural technologies that address critical needs for innovation and traceable metrology, process control and quality in manufacturing at the nanoscale.

    • Study fundamental tip surface interactions that affect the uncertainty of dimensional scanning probe measurements.

    • Provide SPM-based dimensional calibrations from micrometers to 0.1 nanometer.

    Created April 19, 2013, Updated February 28, 2019